Decoding a Musician’s Foot Drop: Fibular Neuropathy Masquerading as Spinal Stenosis

Case Diagnosis: Isolated right fibular neuropathy at the knee in a 76-year-old male with bilateral knee arthroplasty and lumbar stenosis.

Case Description or Program Description: A 76-year-old male professional musician with a history of bilateral knee arthroplasty and an L5 lumbar decompression presented with a painless right foot drop. Notably, he had a prior left foot drop with prolonged recovery following the lumbar decompression 2 years ago. Exam showed 3/5 dorsiflexion and big toe extension with 4/5 eversion and 5/5 inversion strength. MRI revealed bilateral right greater than left L5-S1 foraminal stenosis with grade 1 spondylolisthesis for which he was recommended another spine surgery.

Setting: Outpatient sports medicine clinic.

Assessment/Results: The electrodiagnostic study revealed decreased right superficial fibular sensory nerve amplitude, bilaterally reduced fibular compound muscle action potential amplitudes with slowed conduction but no focal block, and abnormal spontaneous activity in the right tibialis anterior and extensor digitorum brevis. Findings were consistent with right fibular neuropathy at the knee, with ongoing denervation but no radiculopathy or tibial neuropathy. MR neurogram showed an increased signal in the common fibular nerve extending from the bifurcation to the fibular tunnel, consistent with mild neuropathy and hyperintensity within the anterior compartment of the right proximal leg associated with denervation change.

Discussion (relevance): This case highlights the challenge of distinguishing spinal stenosis from fibular neuropathy in painless foot drop. While L5-S1 stenosis could cause radiculopathy, the absence of tibial nerve involvement and focal electrodiagnostic abnormalities at the fibular nerve suggested a peripheral etiology. Differentiating these conditions is crucial, as stenosis may require surgical decompression, while fibular neuropathy is often managed conservatively with bracing and physical therapy to prevent further nerve compression.

Conclusions: This case underscores the importance of electrodiagnostic testing and clinical correlation in evaluating lower extremity weakness.